Ultrasounds: Are They Really Necessary?

When I joined our practice in 1988, most obstetricians did not have ultrasound machines in the office.

The first prenatal visit occurred at 8 or 9 weeks gestation, and included both a thorough history and a physical exam with a uterine evaluation. If everything was in order, patients left with an appointment for a four-week follow-up and a lab slip. At that time, ultrasounds were not routine. In fact, it was not uncommon for a low-risk patient to go to term without ever seeing images of her baby.

Today, however, ultrasounds are routine and expected practices, conducted once at that very first visit and at least two more times throughout the pregnancy (more often if the pregnancy is high-risk).

Over the last ten years, there has been intense debate in the United States about the necessity of multiple routine ultrasounds. Does every pregnant woman need an ultrasound? If so, how many are appropriate? The answers, according to Dr. Roy Filly, an internationally recognized authority on obstetrical ultrasounds, will surprise you:

The National Institutes of Health (NIH) published a list of indications for sonography in pregnant American women. The list is so comprehensive that it is easier to state which pregnant women are not considered candidates for the test. Simply stated, if a pregnant woman is young (but not too young) and healthy; has a firm recollection of the dates of her last normal menstrual period; goes for examination by her obstetrician early in pregnancy; has completely unremarkable physical examination findings and medical, family, and obstetric histories; meets every milestone during her pregnancy; and has no unusual laboratory findings, then she is not a candidate for sonography.

Now, let’s look at the facts:

  • Ultrasounds can diagnose many major fetal abnormalities, and 90 percent of babies born with abnormalities are born to women with no risk factors.
  • Ultrasounds only accurately diagnose major abnormalities with an overall sensitivity of 40.4 percent, but as low as 15% when the examiner is not well trained.
  • Women should be aware of ultrasound’s limitations in diagnosing congenital abnormalities.
  • Ultrasounds primarily reduce the rate of perinatal deaths through termination of babies with congenital malformations; they do not reduce perinatal morbidity.
  • Screenings detect twins/triplets, birth defects and intrauterine growth restriction, but the direct health benefits of having this information is unproven.
  • Because ultrasounds can interact with biological tissues by mechanical and thermal processes, some experts believe they should be restricted to medical indications, by trained professionals, for as short a period and as low an intensity as possible.
  • Uncertain ultrasound results can become a source of anxiety and distress for expectant parents.
  • If a woman meets Dr. Filly’s criteria above, not doing an ultrasound during pregnancy is reasonable.
  • It is best to limit repeat ultrasounds to only those that will affect the way a pregnancy is managed.

The truth is, there are many pregnant women who, according to the criteria above, do not require even one ultrasound. But it is unlikely that either these women or their doctors would accept this recommendation because we are accustomed to having the information ultrasounds can provide.

For more about this topic, see Obstetrical Sonography: The Best Way to Terrify a Pregnant Woman and  Your Baby’s Kidneys: Hydronephrosis/Pelviectasis.


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